Over the last several years we have examined the hypothesis that the inflammatory bowel diseases, ulcerative colitis and Crohn's disease, are due to an abnormal mucosal immune response to one or more ubiquitous antigens in the mucosal environment. During this period we explored this possibility by measuring lymphokine production by lymphocytes present in mucosal biopsies of patients. In initial studies we developed a quantitative reverse transcription polymerase chain reaction (PCR) method based on the use of varying amounts of "standard" mRNA constructs that are co-amplified with the"unknown" mRNA in specimens; amplification of "unknown" that produces a signal equivalent to "standard" of known initial concentration provides a firm estimate of "unknown" initial concentration. The method was developed in a way that allows standards for four different lymphokines to be added simultaneously and then amplified separately, depending on the primers added. Finally, mRNA transcription was normalized for the number of lymphocytes present in intestinal tissue by quantitating TCR mRNA transcription. We found that IL-2 mRNA transcription in inflamed tissue of patients with Crohn's disease was very considerably elevated as compared to uninflamed tissue and tissue from control individuals. In contrast, IL-2 mRNA transcription from inflamed tissue of patients with ulcerative colitis was normal. Finally, IL-2 MRNA transcription of peripheral blood lymphocytes was low and not significantly different in all groups of patients. These studies establish, therefore, that: 1) Crohn's disease is associated with increased IL-2 production; and 2) Crohn's disease and ulcerative colitis are, from an immunologic point of view, very different disease processes. In other, complementary studies, PCR-based quantitation of IFN-gamma, IL-4 and IL-5 in intestinal cells and peripheral blood lymphocytes (PBL) was performed. It was established that IL-2, IFN- gamma and IL-5 production by normal intestinal T cells is far higher than in PBL, whereas IL-4 is produced by PBL, but usually not by the intestinal cells. These studies set the stage for quantitative studies of IFN-gamma, IL-4 and IL-5 in IBD.